1. Field of the Invention
This invention relates to a computer peripheral device and, more particularly, to an apparatus and system for controlling power to the peripheral device.
2. Background of the Relevant Art
The concept of providing multiple modes of operation within a laptop personal computer (PC) is well known. Laptop personal computers often utilize a power management system which controls power to various devices within the laptop computer. To conserve battery power, the power management system continuously monitors various circuit functions of the computer such that devices which are not in use are disconnected from the power source or undergo reduced power consumption. As described in U.S. Pat. No. 5,167,024 to Smith, et al. (incorporated herein by reference), various devices are deactivated or placed in a stand-by state depending upon the mode of operation chosen and the amount of power necessary for the devices.
The United States Environmental Protection Agency (EPA) has recently launched an energy conservation program which would borrow many concepts earlier developed in the power management of laptop computers. In particular EPA wishes to encourage computer manufacturers to introduce energy-efficient desktop personal computers and thereby reduce air pollution associated with electricity generation. With personal computer use on the rise, it is imperative that computer energy consumption be monitored and controlled. In order to meet the guidelines set by the EPA, it would be advantageous to present desktop computers which consume very little power (e.g., less than 30 watts) when placed in a low power mode of operation.
A large majority of power consumed by a desktop computer is by the various peripheral devices connected to the computer. For example, a conventional cathode ray tube (CRT) requires energy not only to drive the electrons from the cathode, but it also requires energy to accelerate the electrons from the cathode as well as energy to deflect or scan the electrons across the phosphor screen. Other peripheral devices such as the computer printer, e.g., impact printer, dot matrix printer, ink jet printer, thermal printer and laser printer require energy to drive the impact units, deflect the ink jet spray nozzles, heat the thermal printer printhead, and modulate the laser beam across the print surface at high speeds. Other peripheral devices such as CD-ROMs, disk drives, tape units, modems, etc., also require a large portion of the total energy consumed by the personal computer. As defined herein, "peripheral device" refers to any device which can be controlled and monitored by a personal computer. A peripheral device includes a visual display, a memory device, or any device which can present an output or input from or to the personal computer as a result of instruction sets stored within the computer.
To reduce power consumption of a personal computer, it is therefore important that power consumption within the peripheral device be monitored and controlled depending upon its state of operation. During times in which the devices are not being used, the devices should be turned off. For example, if the CRT screen is not instructed to change after a set time has elapsed, it should be disconnected from the ac power supply, or "powered down". Likewise, a printer, tape drive unit, CD-ROM, modem, or disk drive which is not being used within a set period of time should also be powered down. In order to power down the periphery devices, it is important to avoid having to retrofit existing host computers or peripheral devices. Instead, it would be advantageous to utilize existing host output for controlling existing peripheral devices without having to add to or change the numerous host and peripheral units already in existence. Accordingly, the power management system must be presented as a unit separate from the host and/or peripheral device. Furthermore, the power management system must be able to discontinue ac power sent to the peripheral device based upon the presence of or absence of signals readily available at the output of the host. Furthermore, the control unit must operate within the guidelines set by the EPA and any proposals set forth by the Video Electronics Standards Association (VESA) for disconnecting power within a host peripheral unit when the unit is not or will not be in use.